This invention relates to a process for the synthesis of optically active anthracyclinones of the formula III: ##STR1## which compounds are key intermediates from which compounds of the formula I: ##STR2## wherein:
(A) R.sub.1 is hydrogen and R.sub.2 and R.sub.3 are the same and are both hydrogen or methyl, methoxy, chlorine or bromine;
(B) R.sub.2 and R.sub.3 are both hydrogen and R.sub.1 is methyl, methoxy, chlorine or bromine; and
(C) R.sub.1 and R.sub.3 are both hydrogen and R.sub.2 is methoxy are obtained. These compounds of formula I can be obtained, for example, by bromination of the corresponding compound of formula III in the 7-position, followed by hydrolysis (A. S. Kende et al. J. Amer. Chem. Soc., 1976, 98, 1967).
Compounds of the Formula I, when condensed with (-)daunosamine give rise to glycosidic compounds which have shown therapeutic activity in the treatment of human and animal tumors. (See co-pending application, Ser. No. 579,901, now U.S. Pat. No. 4,046,878.)
The condensation of hydroquinone with phthalic anhydride in the presence of AlCl.sub.3 --NaCl at 240.degree. C. to give quinizarin has been reported (Chem. Ber., 1929, 62, 512). Similarly, the condensation of phthalic anhydrides with substituted hydroquinones in the presence of AlCl.sub.3 --NaCl at 200.degree. C. for two hours to give dihydroxy-anthraquinones has been reported (Chem. Ber., 1963, 96, 2407). The literature is, however, silent concerning the possibility of a reaction between a phthalic anhydride and the less reactive 1,4-dialkoxybenzenes.